Bone conduction microphones are known in the art and are used in communication systems for the transmission of speech. When a person speaks the cranial bones vibrate in accordance with the sounds that are produced by the person's vocal cords. Bone conduction microphones detect vibrations in the user's cranial bones and convert the vibrations to electrical signals that can be communicated to a two way radio. Bone conduction microphones are especially useful in noisy environments such as, for example, in helicopters, at fire sites, at construction sites, etc., where typical microphones may pick up and transmit a significant amount of ambient noise. Many of these environments require a user to where a protective helmet that has an adjustable headband.
Bone conduction microphones must firmly engage or abut the bone through which the vibrations are traveling for the bone conduction microphone to consistently and reliably detect the vibrations and convert the detected vibrations to electrical signals.
Attempts have been made to attach bone conduction microphones to protective helmets. See for example U.S. Pat. No. 6,298,249 (the '249 patent) in which a bone conduction microphone is mounted on the napestrap of the helmet. The napestrap is the portion of the headband that is generally located in the rear of the helmet and is positioned over the nape of the neck.
These devices, however, include multiple movable parts that must be correctly adjusted for the bone conduction microphone to function properly. For example, the assembly of the '249 patent includes a sliding mechanism that must be closed around a ratchet sleeve, carried on the helmet's napestrap. A ratchet sleeve is a sleeve carried by the napestrap portion of the headband. The ratchet sleeve has an adjustment knob that rotates to increase/decrease the size of the headband. In addition, a screw mechanism must be tightened to secure the assembly to the ratchet sleeve. Further, the microphone is on a separate adjustable flange and must be adjusted to fit the user's head, and a screw mechanism needs to be tightened to retain the microphone in its adjusted position.
Moreover, these devices do not place the microphone in an optimal position to consistently and reliably detect the vibrations in the cranial bones. Further the position of the microphone may need to be adjusted during use, which is impossible, or at least very inconvenient, in many circumstances, such as while fighting a fire, or in the middle of a rescue attempt. In addition, it is not easy and/or convenient to secure these devices to a helmet. Finally, these devices limit the placement of a speaker to one side of the helmet.